Resolve DTLS cookie and version before session resumption.

Session resumption involves a version check, so version negotiation must
happen first. Currently, the DTLS implementation cannot do session
resumption in DTLS 1.0 because the ssl_version check always checks
against 1.2.

Switching the order also removes the need to fixup ssl_version in DTLS
version negotiation.
Signed-off-by: NKurt Roeckx <kurt@roeckx.be>
Reviewed-by: NViktor Dukhovni <viktor@openssl.org>

RT: #4392, MR: #2452

ssl/statem/statem_srvr.c

@@ -1152,6 +1152,38 @@ MSG_PROCESS_RETURN tls_process_client_hello(SSL *s, PACKET *pkt)
         extensions = *pkt;
     }
 
+    if (SSL_IS_DTLS(s)) {
+        /* Empty cookie was already handled above by returning early. */
+        if (SSL_get_options(s) & SSL_OP_COOKIE_EXCHANGE) {
+            if (s->ctx->app_verify_cookie_cb != NULL) {
+                if (s->ctx->app_verify_cookie_cb(s, PACKET_data(&cookie),
+                                                 PACKET_remaining(&cookie)) == 0) {
+                    al = SSL_AD_HANDSHAKE_FAILURE;
+                    SSLerr(SSL_F_TLS_PROCESS_CLIENT_HELLO,
+                           SSL_R_COOKIE_MISMATCH);
+                    goto f_err;
+                    /* else cookie verification succeeded */
+                }
+            /* default verification */
+            } else if (!PACKET_equal(&cookie, s->d1->cookie,
+                                     s->d1->cookie_len)) {
+                al = SSL_AD_HANDSHAKE_FAILURE;
+                SSLerr(SSL_F_TLS_PROCESS_CLIENT_HELLO, SSL_R_COOKIE_MISMATCH);
+                goto f_err;
+            }
+            s->d1->cookie_verified = 1;
+        }
+        if (s->method->version == DTLS_ANY_VERSION) {
+            protverr = ssl_choose_server_version(s);
+            if (protverr != 0) {
+                SSLerr(SSL_F_TLS_PROCESS_CLIENT_HELLO, protverr);
+                s->version = s->client_version;
+                al = SSL_AD_PROTOCOL_VERSION;
+                goto f_err;
+            }
+        }
+    }
+
     s->hit = 0;
 
     /*
@@ -1198,39 +1230,6 @@ MSG_PROCESS_RETURN tls_process_client_hello(SSL *s, PACKET *pkt)
         }
     }
 
-    if (SSL_IS_DTLS(s)) {
-        /* Empty cookie was already handled above by returning early. */
-        if (SSL_get_options(s) & SSL_OP_COOKIE_EXCHANGE) {
-            if (s->ctx->app_verify_cookie_cb != NULL) {
-                if (s->ctx->app_verify_cookie_cb(s, PACKET_data(&cookie),
-                                                 PACKET_remaining(&cookie)) == 0) {
-                    al = SSL_AD_HANDSHAKE_FAILURE;
-                    SSLerr(SSL_F_TLS_PROCESS_CLIENT_HELLO,
-                           SSL_R_COOKIE_MISMATCH);
-                    goto f_err;
-                    /* else cookie verification succeeded */
-                }
-            /* default verification */
-            } else if (!PACKET_equal(&cookie, s->d1->cookie,
-                                     s->d1->cookie_len)) {
-                al = SSL_AD_HANDSHAKE_FAILURE;
-                SSLerr(SSL_F_TLS_PROCESS_CLIENT_HELLO, SSL_R_COOKIE_MISMATCH);
-                goto f_err;
-            }
-            s->d1->cookie_verified = 1;
-        }
-        if (s->method->version == DTLS_ANY_VERSION) {
-            protverr = ssl_choose_server_version(s);
-            if (protverr != 0) {
-                SSLerr(SSL_F_TLS_PROCESS_CLIENT_HELLO, protverr);
-                s->version = s->client_version;
-                al = SSL_AD_PROTOCOL_VERSION;
-                goto f_err;
-            }
-            s->session->ssl_version = s->version;
-        }
-    }
-
     if (ssl_bytes_to_cipher_list(s, &cipher_suites, &(ciphers),
                                  is_v2_record, &al) == NULL) {
         goto f_err;